Complete primary structure of rainbow trout type I collagen consisting of α1(I)α2(I)α3(I) heterotrimers

The subunit compositions of skin and muscle type I collagens from rainbow trout were found to be alpha1(I)alpha2(I)alpha3(I) and [alpha1(I)](2)alpha2(I), respectively. The occurrence of alpha3(I) has been observed only for bonyfish. The skin collagen exhibited more susceptibility to both heat denaturation and MMP-13 digestion than the muscle counterpart; the former had a lower denaturation temperature by about 0.5 degrees C than the latter. The lower stability of skin collagen, however, is not due to the low levels of imino acids because the contents of Pro and Hyp were almost constant in both collagens. On the other hand, some cDNAs coding for the N-terminal and/or a part of triple-helical domains of proalpha(I) chains were cloned from the cDNA library of rainbow trout fibroblasts. These cDNAs together with the previously cloned collagen cDNAs gave information about the complete primary structure of type I procollagen. The main triple-helical domain of each proalpha(I) chain had 338 uninterrupted Gly-X-Y triplets consisting of 1014 amino acids and was unique in its high content of Gly-Gly doublets. In particular, the bonyfish-specific alpha(I) chain, proalpha3(I) was characterized by the small number of Gly-Pro-Pro triplets, 19, and the large number of Gly-Gly doublets, 38, in the triple-helical domain, compared to 23 and 22, respectively, for proalpha1(I). The small number of Gly-Pro-Pro and the large number of Gly-Gly in proalpha3(I) was assumed to partially loosen the triple-helical structure of skin collagen, leading to the lower stability of skin collagen mentioned above. Finally, phylogenetic analyses revealed that proalpha3(I) had diverged from proalpha1(I). This study is the first report of the complete primary structure of fish type I procollagen.

Characterization of a rainbow trout matrix metalloproteinase capable of degrading type I collagen

Matrix metalloproteinases (MMPs) are widely distributed in vertebrate tissues and form a large family consisting of at least four distinct subfamilies. Higher vertebrate MMP-13 is well-known as collagenase-3, which represents the third member of a collagenase subfamily. In this study, we cloned cDNA coding for a unique fish homologue of human MMP-13 from a rainbow trout fibroblast cDNA library. The cDNA was 2.1 kb long and contained an open reading frame encoding a protein of 475 amino acids. The catalytic domain of the protein was 66% identical to the human counterpart with the greatest degree of identity occurring in the zinc binding site. In addition, it possessed three amino-acid residues (Tyr122, Asp233 and Gly235) characteristic of the collagenase subfamily, together with a six residue insertion which did not occur in the collagenase subfamily. Then the isolated cDNA was expressed in Escherichia coli and the recombinant protein was found to degrade gelatin and skin type I collagen. It is worth noting that rainbow trout type I collagen was more susceptible to proteolysis with the recombinant protein when compared with the calf one. It appeared that the recombinant protein also cleaved the nonhelical regions of rainbow trout muscle type V collagen. These results have revealed that the cDNA encodes a unique MMP-13 of rainbow trout. This is the first report of cDNA coding for fish MMP capable of degrading type I collagen.

Effects of ergothioneine, cysteine, and glutathione on nitrosation of secondary amines under physiologic conditions

The effects of ergothioneine, cysteine, and glutathione, which are naturally occurring sulfhydryl compounds, on the aerobic and anaerobic nitrosation of dimethylamine were studied at pH 2.0-7.0 and at 37 degrees C. Under aerobic conditions, ergothioneine increased the formation of dimethylnitrosamine (DMN) at all pH values tested, cysteine and glutathione had the same effect at pH 4.0-6.0, and cysteine formed DMN at pH 7.0. However, as compared to controls cysteine showed no increased effect in an O2 atmosphere at pH 6.0. The effects of sulfhydryl compounds on anaerobic nitrosation were more significant (p < 0.001) than on aerobic nitrosation, probably because these sulfhydryl compounds, except ergothioneine, are easily oxidized. Ergothioneine increased aerobic nitrosation almost as strongly as anaerobic nitrosation. The effects of sulfhydryl compounds, especially ergothioneine, on nitrosation at physiologic pH and temperature might be significant in the in vivo formation of N-nitrosamines in the hemorrhage or ulcerous gastrointestinal tract or injured organs.

Formation of N-nitrosamines from seconday animes and nitrite by resting cells of Escherichia coli B

In the presence of resting cells of Escherichia coli B, the formation of N-nitrosamines from nitrite and secondary amines, such as dimethylamine and piperidine, was proportional to the incubation time and to the cell concentration. Optimum pH was 8.0. Boiled cells were incapable of nitrosating secondary amines. Although these experiments were carried out by using intact cells of E. coli B, the reaction followed Michaelis-Menten kinetics, and the apparent Km values calculated from Lineweaver-Burk plots were 0.12 +/- 0.03 M for dimethylamine and 0.07 +/- 0.02 M for nitrite. The apparent Km for piperidine was 0.15 +/- 0.05 M. The nitrosation was inhibited by high substrate concentrations. These results suggested that the formation of n-nitrosamines by resting cells of E. coli B apparently depends on their enzyme activities.